This invention concerns a process for making certain polymeric inorganic-organic compositions, occasionally also referred to herein as hybrid compositions or hybrid materials, which consist essentially of an inorganic network portion and an organic polymer portion, those two components being intimately combined to the point that they cannot be readily separated from each other by known physical processes without substantial destruction of one of those components.
It is well known to make gels of certain inorganic materials, e.g., of silica, by hydrolysis of the corresponding alkoxy compounds. For example, tetraalkoxysilanes are hydrolyzed to a material having ##STR1## groups. Such reactions require cosolvents for the water and the tetraalkoxysilane and are catalyzed by either acids or alkalies. It has recently been discovered, however, that strong carboxylic acids, especially, e.g., formic acid, can rapidly react with tetraalkoxysilanes to form inorganic networks without the need for either cosolvents or water as a reactant. The acid is not simply a catalyst; it must be present in at least a stoichiometric amount.
It is known to blend organic polymers with inorganic fillers either in order to improve some properties of those polymers or to reduce the cost of the polymeric compositions by substituting cheaper inorganic materials for more expensive organic materials. Typical inorganic fillers can be either particulate or fibrous and can be derived from a variety of materials, including naturally occurring minerals and glass. In most cases, the inorganic filler is discontinuous and can be separated from the polymer matrix by simple mechanical processes or by extraction of the polymer component therefrom. Addition of fillers to organic polymers frequently has the undesirable effect of reducing toughness.
It is believed that certain properties of polymers could be significantly improved, and new properties could be imparted to polymers by providing hybrid inroganic-organic polymer compositions comprising continuous inorganic networks, as described above. Some such compositions are described, for example, in the application Ser. No. 07/725,169 of I. David, now abandoned. However, since David's process requires substantial water solubility of the polymer component, there still is a need for a practical process for making such hybrid compositions.